Long-time storage of entangled logical states in decoherence-free subspaces

TL;DR

This paper demonstrates long-duration storage of entangled logical states in decoherence-free subspaces of ions, achieving about one hour of coherence, which advances quantum memory technology for quantum computing and communication.

Contribution

The study introduces a method for encoding entangled states into second-order DFS with enhanced noise suppression, extending storage lifetime significantly.

Findings

Achieved approximately one hour of entangled state storage.

Demonstrated the advantage of second-order DFS in noise suppression.

Implemented crosstalk-free sympathetic cooling and multi-state detection.

Abstract

The maintenance of quantum entanglement lays the elementary building block of quantum information processing, requiring an integration of long coherence time, sufficient storage capacity, and high-fidelity entangling gates. Here we encode two-qubit entangled states into the decoherence-free subspaces (DFS) of four ions in a cryogenic trap. By crosstalk-free sympathetic cooling under dual-type encoding and multi-state detection which discards the collision-induced leakage error, we achieve a storage lifetime of about one hour for the entangled logical states. We further study the second-order DFS and show its advantage in suppressing the spatially nonuniform noise over the first-order DFS. Our work paves the way for applications of DFS quantum memories in quantum computing, quantum network and precision measurement.